Does the giver of charity receive the full reward for the charity if he paid the entire amount by mistake, when he intended to pay only a portion of it?

If you waive a debt with the intention of giving charity, it is counted as a charity for you, and you will be rewarded for it, based on the Prophet's (peace be upon him) saying: "Deeds are only by intentions, and every person will have what he intended." The Quran encourages waiving debts and calls it charity in Allah's (the Exalted) saying: "And if there is one in [financial] difficulty, then [let there be] postponement until [a time of] ease. But if you give [it in charity] as a charity, it is better for you, if you only knew."